Continuous high-decarburized steel production method and system

Abstract

A continuous high-decarburized steel production system comprises a plurality of operating stations (10, 20, 30, 40, 50, 60) arranged in succession along a movement direction (X) of semi-finished steel products, comprising: a smelting furnace (10) configured to generate a metal bath; a multi-strand continuous casting machine (15) configured to produce a plurality of semi-finished steel products (5); a conveying unit (60) of semi-finished steel products (5) configured to convey the semi-finished steel products (5) from the multi-strand continuous casting machine (15) to the subsequent operating stations; a reheating furnace (40) configured to heat the semi-finished steel products (5) to a predetermined temperature value; a welding station (30) configured to weld together the semi-finished steel products (5) to obtain a continuous semi-finished product (7); and a continuous rolling unit (20) configured to roll the continuous semi-finished product (7).

Description

Technical Field

[0001] This invention relates to the field of steel production, and in particular to a method and system for continuous high decarburization steel production. Background Technology

[0002] Steel production has a significant impact on global energy demand and hazardous emissions, accounting for approximately 8% of global energy consumption and 7% of CO2 emissions. This significant environmental impact is primarily attributed to the industry's heavy reliance on coal. Steel production involves both the use of iron ore and the recycling of scrap steel; primary steel production is a coal-intensive process, while secondary steel production mainly uses electricity. Despite some progress in energy efficiency, the steel industry still faces substantial challenges, as every ton of steel produced generates significant CO2 emissions.

[0003] In the short term, traditional approaches that improve technological performance and reduce demand by increasing material utilization efficiency will play a key role. In the medium to long term, CO2 capture and utilization (CCUS) technology, and the transition from coal to natural gas, hydrogen, and bioenergy, are becoming increasingly important.

[0004] However, despite some progress, the industry still faces challenges in reducing energy intensity and emissions; and the emissions reductions achieved to date are insufficient to meet the targets set by the international agreement.

[0005] Therefore, there is a need to develop innovative technologies that can reduce emissions from steel production in the medium to long term. Summary of the Invention

[0006] The overall objective of this invention is to meet this need by providing a method and system that can reduce the environmental impact of continuous steel production by minimizing CO2 emissions, while ensuring high productivity and efficiency.

[0007] In view of this purpose, the inventors have considered implementing the continuous high decarburization steel production method and system as described in claims 1 and 7 according to the present invention.

[0008] The dependent claims further define other innovative features of the invention.

[0009] Further features and advantages of the present invention will become apparent from the following detailed description. Attached Figure Description

[0010] Reference will now be made in detail to various embodiments of the present invention, one or more of which are illustrated in the accompanying drawings, as follows:

[0011] - Figure 1This is a schematic block diagram of a continuous high-decarburization steel production system according to the present invention;

[0012] - Figure 2 This is a schematic block diagram of a known type of steel production equipment, showing the production volume; and

[0013] - Figure 3 This is a schematic block diagram of a steel production apparatus according to the present invention, showing the production capacity.

[0014] Where possible, the same reference numerals are used in the figures to identify common, identical elements for ease of understanding. It should be understood that elements and features in one embodiment can be readily integrated into other embodiments without further explanation. Detailed Implementation

[0015] Each example is for illustrative purposes only and is not intended to be limiting. For instance, technical features shown or described as belonging to one embodiment may be implemented in other embodiments or combined with other embodiments to form new embodiments. It should be understood that the present invention covers such modifications and variations.

[0016] According to the present invention, a continuous high decarburization steel production system (generally referred to as Figure 1) includes multiple operating stations arranged sequentially along the movement direction X of the semi-finished steel.

[0017] The steel production system 1 includes a smelting furnace 10 (e.g., an electric arc furnace EAF) configured to produce a molten pool of metal with a predetermined chemical composition.

[0018] The steel production system 1 also includes a multi-strand continuous casting machine 15, which is connected to the melting furnace 10 and includes multiple parallel continuous casting lines 17; each continuous casting line is configured to use the molten metal in the melting furnace 10 to produce multiple semi-finished steel products (e.g., billets 5) with finished lengths.

[0019] The steel production system 1 also includes a billet rolling unit 20, which is arranged downstream of the melting furnace 10 along the direction of movement X of the semi-finished steel. Preferably, the rolling unit 20 includes at least one rolling mill, more preferably a single rolling mill, configured to roll the semi-finished steel from the continuous casting line 17. According to a particularly advantageous feature of the invention, the rolling unit 20 is a rolling unit for continuous rolling operation.

[0020] This feature is particularly advantageous, especially in reducing CO2 emissions, which in turn facilitates the decarburization of the steel production system 1 of the present invention.

[0021] According to an embodiment of the present invention, the steel production system 1 includes a welding station 30, which is arranged downstream of the melting furnace 10 and upstream of the rolling unit 20 along the direction of movement X of the semi-finished steel. The welding station 30 is configured to weld billets 5 from the casting line 17 together and arrange them sequentially along the direction of movement X of the semi-finished products to form a single continuous semi-finished steel product 7, which is then supplied to the rolling unit 20.

[0022] According to the implementation scheme, the steel production system 1 includes a billet conveyor 5 arranged upstream of the welding station 30, configured to collect multiple billets 5 produced by the various casting lines 17 (which were originally arranged along multiple conveying paths) onto a single conveying path, thereby arranging these billets sequentially in rows along this single conveying path. This conveyor can be arranged after the reheat furnace 40, inside the reheat furnace 40, or at any other location within the steel production system 1 along the semi-finished product movement direction X between the welding station 20 and the multi-strand casting machine 15, all without departing from the scope of this invention.

[0023] Therefore, the welding station 30 enables the rolling mill to continuously roll the semi-finished steel 7 even when it is fed by multiple casting lines 17.

[0024] This feature offers significant advantages in many ways, including improved equipment productivity. For example, refer to... Figure 2 It is known that existing production equipment for continuous rolling includes smelting furnaces and continuous casting machines for producing continuous semi-finished products. However, such solutions have some drawbacks, including the requirement that each rolling mill has a continuous casting line because the semi-finished products are produced continuously. This limitation necessitates adding more continuous casting lines and corresponding rolling mills when increasing equipment capacity.

[0025] like Figure 3 As shown, the solution of the present invention allows multiple casting lines 17 to be associated with a single rolling mill, thereby improving the production efficiency of the steel production system 1.

[0026] Furthermore, in terms of the amount of steel produced per unit time (quality value), the output of a continuous casting line often does not match the output of a rolling mill per unit time (quality value) (in fact, this mismatch occurs frequently). In other words, if the continuous casting line produces fewer tons of steel than the rolling mill can produce, the production equipment will face significant inefficiencies and / or be forced to increase the casting speed.

[0027] Therefore, another advantage of the present invention is that it allows steel to be cast at the most suitable casting speed according to the type of alloy formed, to cast a wider range of steel alloys, so that the continuous casting speed can be adjusted to the technically most suitable speed without limitation or at least without risky forced adjustments, and can reduce system wear and maintenance costs.

[0028] According to an embodiment of the invention, the steel production system 1 includes a reheating furnace 40 arranged upstream of the welding station 30 along the direction of movement X of the semi-finished steel. The reheating furnace 40 is configured to maintain or raise the temperature of the billet 5 to a predetermined value. Preferably, the predetermined temperature value corresponds to (or is close to) a rolling temperature sufficient to roll the semi-finished steel in the rolling mill of the rolling unit 20.

[0029] Preferably, the reheat furnace 40 is a combustion heating system comprising a furnace through which billets 5 from casting line 17 pass. According to this embodiment, the reheat furnace 40 includes one or more flameless burners configured to generate hot flue gas with a low oxygen content within the furnace. Preferably, these burners are powered by a fuel mixture ranging from natural gas to hydrogen, thereby reducing the total CO2 produced by the system of the present invention.

[0030] According to other embodiments, the steel production system 1 may also include a solid oxide electrolytic cell (SOEC) connected to the reheat furnace 40.

[0031] Alternatively, the reheating furnace 40 can be an induction furnace.

[0032] According to other embodiments, the steel production system 1 includes an electric heating unit 45, preferably a direct heating unit utilizing the Joule effect.

[0033] The electric heating unit 45 may be an electric furnace independent of the reheating furnace 40, and is arranged downstream of the reheating furnace 40 along the direction of movement X of the semi-finished steel. In other embodiments, the heating unit 45 is integrated inside the reheating furnace 40.

[0034] The use of electric heating unit 45 further improves the decarburization level of the steel production system 1 of the present invention because it reduces the use of reheat furnace 40, thereby reducing its energy consumption and CO2 emissions. In addition, electric heating unit 45 can be selectively activated (i.e., started on demand) and can heat billet 5 at higher temperatures and faster rates than combustion furnaces, thereby optimizing the production cycle and reducing the overall energy consumption of steel production system 1.

[0035] According to some embodiments, the steel production system 1 includes a billet buffer device (not shown) capable of regulating the flow of billets 5 within the reheating furnace 40. Preferably, the buffer device is arranged upstream of the reheating furnace 40 along the direction of movement X of the semi-finished steel and configured to reduce or increase the amount of billets 5 entering the reheating furnace based on whether the quantity of billets produced by the casting line 17 of the casting machine 15 is greater or less than the production capacity of the rolling unit 20. For example, the buffer device may include a storage area for storing or removing billets 5 from the casting line 17, thereby enabling the removal or addition of billets 5 from or to the reheating furnace 40, respectively.

[0036] According to some implementation schemes, the billet buffer device includes the billet conveyor described above.

[0037] According to other embodiments, the steel production system 1 includes a preheating unit 50, which is arranged upstream of the reheating furnace 40 along the direction of movement X of the semi-finished steel.

[0038] According to an embodiment of the present invention, both the reheating furnace 40 and the preheating unit 50 include a combustion heating system, a direct electric heating system utilizing the Joule effect, an induction heating system, or a hybrid heating system including a combustion system and an electric heating and / or induction heating system.

[0039] Therefore, the production system according to the present invention can achieve a high degree of operational flexibility, thereby optimizing the thermal management of semi-finished products according to operating conditions and specific production needs.

[0040] According to other embodiments, the steel production system 1 may further include a billet conveying unit 60; this conveying unit 60 is arranged downstream of the continuous casting line 17 of the multi-strand continuous casting machine 15 and upstream of the preheating unit 50 or reheating furnace 40, along the direction of movement X of the semi-finished steel. The conveying unit 60 is configured to convey the billet 5 from the continuous casting line 17 to subsequent operating stations. Preferably, the conveying unit 60 includes a billet conveyor with multiple roller conveyor lines and a roller conveyor table.

[0041] According to the implementation plan, the billet conveying unit 60 includes a billet buffer device configured to address production imbalances between the casting machine 15 and subsequent processing stations, as well as to address any production interruptions in the steel production system 1.

[0042] Preferably, the billet conveying unit 60 includes a heat shield configured to retain the heat of the billet 5. These heat shields are arranged on each line of the billet roller conveyor 5, as well as on the roller conveyor table and buffer device.

[0043] According to a continuous and efficient decarburized steel production method of the present invention, the first step is to produce multiple semi-finished steel products (e.g. billets 5) with finished lengths using a continuous rolling mill 15 fed by a melting furnace 10 (e.g., an electric arc furnace EAF).

[0044] The steel production method includes a second step: rapidly conveying billet 5 from multi-strand continuous casting machine 15 to subsequent operating stations; these operating stations are arranged sequentially along the movement direction X of the semi-finished steel. For example, in this step, billet 5 is conveyed from multi-strand continuous casting machine 15 to reheat furnace 40.

[0045] The rapid conveying step helps to shorten the travel time of the billet 5 produced by the multi-strand continuous casting machine 15 to the subsequent operation station, thereby enabling the billet 5 to retain the residual heat energy in the continuous casting process to the maximum extent.

[0046] The applicant’s experiments showed that the continuous casting temperature of the molten steel was between 1480°C and 1540°C, and the average target temperature at the end of the heating step (i.e., the average rolling temperature) was 1100°C to ensure the nominal production rate of 160 t / h of steel.

[0047] According to the rapid conveying step of the present invention, multiple billets 5 can be conveyed to the reheating furnace 40, the temperature gradient of which fluctuates between two extreme values:

[0048] - Lower limit: The temperature of the billet entering the reheating furnace is 750°C, and the calculated core temperature is approximately 820°C; and

[0049] - Upper limit: The temperature on the side of the billet entering the reheating furnace is 800°C, and the calculated core temperature is approximately 900°C.

[0050] This solution significantly reduces heat loss in downstream steelmaking processes and minimizes delays throughout the entire process chain, thereby reducing the energy required to heat billets and increasing production efficiency. By minimizing billet transport delays and heat loss, it reduces energy consumption for heating billets in the reheat furnace and increases effective capacity; compared to the cold loading path, fuel consumption is reduced by up to 80%, and productivity is increased by over 150%.

[0051] Although conceptually simple, this transfer process faces numerous challenges in practical applications: establishing a flexible and manageable interface between the continuous casting line and subsequent downstream stations; and coordinating equipment with different characteristics and production dynamics.

[0052] According to some implementation schemes, this step includes a simulation program configured to study and simulate various conditions and operating scenarios, and translate the calculation results into layouts and equipment to manage production imbalances unique to continuous casting and rolling mills and optimize the flow of thermal processes.

[0053] The method for producing high-decarburized steel includes a third step: heating the billet 5, wherein the temperature of the billet 5 is increased to a predetermined value, i.e., the final heating temperature value, for example, the rolling temperature value. The final billet heating temperature value is calculated with high precision so that its deviation from the required rolling temperature is kept within ±10°C.

[0054] This step may involve the use of a reheat furnace 40. The reheat furnace 40 includes, for example, a flameless burner, preferably supplied with a fuel mixture selected from the range of natural gas to hydrogen. Such a combustion system produces high-temperature flue gas with low oxygen content within the furnace. For example, experiments have shown that NOx emissions can be kept well below 80 mg / Nm³ under conditions where the oxygen content in the dry flue gas is 5%. 3 At the same time, the combustion air temperature can be much higher than 400°C.

[0055] To balance the overall steel production system's efficiency, the continuous casting process typically involves several casting lines, resulting in a layered distribution of billets 5. Consequently, the temperature of the billets 5 entering the reheating furnace 40 cannot remain constant across the different billets 5 because each billet 5 experiences different transfer times from the casting line 17 to the reheating furnace 40 and is exposed to different cooling conditions. Thermo-numerical simulations for different motion and operating conditions determined the temperature range of the billets 5 at the inlet of the reheating furnace 40 and the estimated temperature gradient within the billet cross-section.

[0056] However, it should be noted that using hydrogen as fuel requires large quantities of hydrogen, which cannot be easily obtained from gas distribution companies and must be produced locally through the installation of electrolysis units. Standard electrolysis technologies, such as alkaline electrolysis, proton exchange membrane (PEM), or anion exchange membrane (AEM) technologies, inevitably suffer from low efficiency, meaning that hydrogen production and self-sufficiency have high levelized costs. These costs have not yet been offset by carbon emission pricing strategies.

[0057] Therefore, embodiments of the present invention further include a step of producing oxygen while heating the billet using a flameless burner. For example, this step may include:

[0058] - In the exhaust gas duct, after passing through a heat recovery system (central heat exchanger, regenerative burner, etc.), the enthalpy of the exhaust gas is recovered from the steam generator as low-temperature steam; and

[0059] - The low-temperature steam is used as an enthalpy source to supply a solid oxide electrolyzer (SOEC) to produce hydrogen (and optionally O2).

[0060] Compared to technologies such as alkaline electrolysis, PEM, or AEM, this step can reduce energy consumption by approximately 20% to 30%.

[0061] Preferably, oxygen can also be recovered for enriching the combustion air, thereby further reducing the fuel consumption of the furnace by 20%.

[0062] Alternatively, pure oxygen can be supplied to oxygen pipelines for smelting operations.

[0063] The high decarburization steel production method includes a fourth step: by welding the billets 5 heated in the aforementioned steps to each other in the welding station 30, the process is changed from intermittent to continuous, thereby obtaining a single continuous semi-finished steel product 7.

[0064] This scheme enables continuous and uninterrupted production, thereby improving the productivity and yield of the steel production system of this invention. Experiments show that eliminating downtime caused by rolling discrete-length billets 5 extends production time and reduces unit energy consumption. Furthermore, compared to conventional rolling processes, welding the billet 5 reduces natural gas consumption for heating the billet 5 in the aforementioned steps by more than 5%, thereby correspondingly reducing CO2 emissions. This step also increases the yield by 2% and further reduces CO2 emissions.

[0065] Finally, in the continuous rolling process, the reduction of rolling errors and the extension of the service life of welding machines and rolling mill components have a positive impact on reducing CO2 emissions by improving the utilization rate of the equipment.

[0066] The continuous production method for high decarburized steel includes a fifth step: rolling a single semi-finished steel product 7 in a continuous rolling unit 20.

[0067] According to an embodiment of the present invention, the continuous production method of high decarburized steel further includes an additional billet preheating step 5 before the third billet heating step 5.

[0068] This step increases and homogenizes the temperature of the billet 5, enabling the reheating furnace to continuously load multiple billets 5 at the same temperature. Furthermore, this step brings the temperature of the billet 5 closer to the temperature required at the outlet of the reheating furnace 40 (i.e., the rolling temperature), thereby reducing the energy consumption required by the reheating furnace 40 and, most importantly, shortening the time required to reach that temperature.

[0069] According to the specific implementation plan, the heating and preheating steps are achieved through an electric heating unit, that is, heating is performed using the Joule effect. This advantage allows the billet to be rapidly heated from ambient temperature to the required rolling temperature.

[0070] The direct heating system utilizing the Joule effect ensures uniform heating across the entire cross-section of the material, thereby significantly reducing the formation of flakes and decarburization. The system employs an inside-out heating method, ensuring rapid and uniform heating; at the end of heating, the internal temperature difference (ΔT) is less than 10 °C.

[0071] This heating system significantly improves the efficiency and flexibility of billet heating, and is especially suitable for heating high-quality steel and special steel. It can not only handle batches of billets of the same size and steel grade smoothly, but also batches of billets of different sizes and steel grades.

[0072] The Joule-effect-based heating system ensures highly efficient energy conversion, converting high-voltage grid power to the required voltage level through three steps, depending on specific heating needs. Its system efficiency can reach 90%, and even 93% under certain conditions. This high efficiency aligns with a technology performance enhancement strategy that envisions gradually reducing energy intensity through improved operation and upgrades to Best Available Technology (BAT).

Claims

1. A continuous high-decarburization steel production system, comprising multiple operating stations (10, 15, 20, 30, 40, 45, 50, 60) arranged sequentially along the movement direction (X) of the semi-finished steel, wherein the operating stations include: - A smelting furnace (10) configured to produce a molten metal pool; - A multi-strand continuous casting machine (15) configured to produce multiple semi-finished steel products (5); - A conveying unit (60) for semi-finished steel is arranged downstream of the multi-strand continuous casting machine (15), which is configured to convey the semi-finished steel (5) from the multi-strand continuous casting machine (15) to the subsequent operating station; - A reheating furnace (40) located downstream of the conveying unit (60) is configured to heat the semi-finished steel (5) to a predetermined temperature value; - A welding station (30) located downstream of the heating furnace (40) is configured to weld semi-finished steel (5) together to obtain continuous semi-finished steel (7); and - A continuous rolling unit (20) located downstream of the welding station (30) is configured to roll a continuous semi-finished steel product (7).

2. The steel production system according to claim 1, characterized in that, The multi-strand continuous casting machine (15) includes multiple parallel continuous casting lines (17), each configured to produce multiple billets (5).

3. The steel production system according to claim 1, characterized in that, The steel production system includes a preheating unit (50) arranged downstream of the conveying unit (60) and configured to heat the semi-finished steel (5) to another predetermined temperature value.

4. The steel production system according to claim 1, characterized in that, The rolling unit (20) includes a rolling mill.

5. The steel production system according to claim 1, characterized in that, The reheating furnace (40) includes a combustion heating system, a direct electric heating system utilizing the Joule effect, an induction heating system, or a hybrid heating system.

6. The steel production system according to claim 3, characterized in that, The preheating unit (50) includes a combustion heating system, a direct electric heating system utilizing the Joule effect, an induction heating system, or a hybrid heating system.

7. The steel production system according to any one of the preceding claims, characterized in that, The steel production system includes a billet buffer device arranged upstream of the reheat furnace (40) along the direction of movement (X) of the semi-finished steel.

8. A continuous production method for high-decarburized steel, comprising the following steps: - Prepare a molten metal pool using a smelting furnace (10); - Using a multi-strand continuous casting machine (15) and a molten metal pool, multiple semi-finished steel products (5) are produced. - The semi-finished steel (5) is heated to a predetermined temperature using a reheating furnace (40); - The heated semi-finished steel pieces (5) are welded together to obtain continuous semi-finished steel pieces (7); and - The continuous semi-finished steel (7) is rolled in the mill row of the continuous rolling unit (20).

9. The method according to claim 8, characterized in that, The method includes a step of regulating the flow of semi-finished steel (5) using a buffer device before the welding step.

10. The method according to claim 8, characterized in that, The heating process utilizes the Joule effect to ensure that the internal temperature difference ΔT is less than 10℃.

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